The present invention relates to an antibacterial composition. More particularly, it relates to an antibacterial composition comprising Nocardicin A or its salt and cycloserine or its salt.
Nocardicin A is known as a valuable antibiotic having antibacterial activities against Gram-positive bacteria and Gram-negative bacteria, especially pathogenic Pseudomonas species, and is disclosed under the code name of the antibiotic FR-1923 substance in literatures, e.g. U.S. Pat. No. 3,923,977 and German Offenlegungsschrift No. 2,242,699, in which said antibiotic is defined by the various physico-chemical properties without the chemical structure thereof, but, as a result of further investigation, its chemical structure has been identified and assigned as follows. ##STR1##
Further, cycloserine is also known as an antibiotic, especially as an antituberculotic agent (vide, e.g. ANTIBIOTICS AND CHEMOTHERAPY Vol. 5, pages 182-205, 1955).
Only for reference to states of the arts, it is noted that said literature (ANTIBIOTICS AND CHEMOTHERAPY Vol. 5, pages 182-205) discloses the synergistic effect of the combination of cycloserine and penicillins, bacitracin, oxytetracycline, chlortetracycline, streptomycin or chloromphenicol against Gram-positive and Gram-negative bacteria. The inventors of the present invention have conducted extensive studies for enhancing the antimicrobial activities of Nocardicin A per se for the therapeutic purpose thereof. As a result of such extensive studies, the inventors of the present invention have finally succeeded in finding that antibacterial activities of Nocardicin A against various Gram-negative bacteria can be remarkably enhanced by combination with cycloserine. That is, the inventors of the present invention have found that Nocardicin A exhibits a synergistic antibacterial activities by combination with cycloserine. On the other hand, it has been noted that antimicrobial activities of Nocardicin A can not be enhanced by combination with the other antibiotics, for example, penicillins, cephalosporins, etc. As explained, enhancement of antimicrobial activities of Nocardicin A by combination with cycloserine and no enhancement thereof by combination with the other antibiotics are new unexpected and surprising findings, and such behaviors of Nocardicin A are due to the unique properties and chemical structure of Nocardicin A.
Accordingly, the antibacterial composition of the present invention is characterized by the synergistic activity against various pathogenic bacteria, especially Gram-negative bacteria such as Pseudomonas aeruginosa, Proteus vulgaris and Escherichia coli.